This invention relates generally to semiconductor structures and devices and to a method for their fabrication, and more specifically to multiple quantum well infrared photodetectors formed using Group III-V and/or Group II-VI periodic table material combinations grown on a compliant substrate.
Semiconductor devices typically include multiple layers of conductive, insulating, and semiconductive layers. Often, the desirable properties of such layers improve with the crystallinity of the layer. For example, the electron mobility and band gap of semiconductive layers improves as the crystallinity of the layer increases. Similarly, the free electron concentration of conductive layers and the electron charge displacement and electron energy recoverability of insulative or dielectric films improves as the crystallinity of these layers increases.
For many years, attempts have been made to grow various monolithic thin films on a foreign substrate, such as silicon (Si). To achieve optimal characteristics of the various monolithic layers, however, a monocrystalline film of high crystalline quality is desired. Attempts have been made, for example, to grow various monocrystalline layers on a substrate such as germanium, silicon, and various insulators. These attempts have generally been unsuccessful because lattice mismatches between the host crystal and the grown crystal have caused the resulting layer of monocrystalline material to be of low crystalline quality.
If a large area thin film of high quality monocrystalline material was available at low cost, a variety of semiconductor devices could advantageously be fabricated in that film at a low cost compared to the cost of fabricating such devices beginning with a bulk wafer of semiconductor material or in an epitaxial film of such material on a bulk wafer of semiconductor material. In addition, if a thin film of high quality monocrystalline material could be realized beginning with a bulk wafer such as a silicon wafer, an integrated device structure could be achieved that took advantage of the best properties of both the silicon and the high quality monocrystalline material.
Accordingly, a need exists for a semiconductor structure that provides a high quality monocrystalline film or layer over another monocrystalline material and for a process for making such a structure.
This structure and process could have extensive applications. One such application of this structure and process involves the formation of quantum well infrared photodetectors. Recently, multi-quantum well structures built using multiple layers of semiconductor materials with alternating band gaps have proven to be applicable in building quantum well infrared photodetectors (QWIPs). An advantage of QWIPs is that they have the ability to sense multiple wavelengths of radiation and output current according to the wavelength absorbed. However, present-day QWIPs are expensive due to high-cost substrates and the requirement of separate CMOS circuits required to sense the output of each QWIP array element.
Accordingly, a need exists for a low cost quantum well infrared photodetector and a process for making the same.